Sweet Corn Pheromone Trap Network

for Western NY - 2007

This is a seasonal scouting report giving growers in the Western New
York area information on the presence of sweet corn pests and recommendations
on scouting and thresholds. The report is written by
Abby Seaman, NYS IPM's Area
Extension Educator for Vegetables.

For 8/21/07

European corn borer catches have decreased substantially at many locations
since last week. New egg masses are still generally easy to find in tassel
emergence and green silk stage fields. The damage I'm seeing to the tassel
in tassel emergence stage fields is mostly caused by western corn rootworm
feeding, and is easily mistaken for ECB feeding, so it's worth looking closely
for larvae when scouting. Corn earworm numbers are not generally increasing,
but numbers are high enough at some locations for a 5-day spray interval
(see table below) in green silk stage fields. Fall armyworm numbers remain
moderate, although 44 were caught at one site this week. Don Sweet reports
that he is finding high numbers of FAW larvae in the emerging tassel in
some fields this week

Split field demonstrations have shown that applying insecticides to sweet
corn for worm control before tassel emergence does not produce better results
than waiting until the recommended tassel-emergence spray timing.

In fields still in the whorl stage when eggs are deposited, larvae move
to the whorl, feed on the foliage and un-emerged tassel, and are found feeding
on the tassel when it emerges.

Larvae feeding in the whorl are protected from insecticide applications
and mortality will not be as high as at tassel emergence, when larvae feeding
in the emerging tassel are exposed to the spray. Fields should be first
scouted for ECB and FAW larvae at early tassel emergence. For corn borers,
look down into emerging tassels for tiny larvae or frass (white to brown
material about the size of fine sand). For armyworms look for ragged feeding
holes and frass pellets the texture of coarse sawdust.

The threshold for ECB and armyworms at tassel emergence is 15% infested
plants.

Before any insecticides have been applied, scouting is fast and easy
because any sign of feeding is an almost sure sign of live larvae, so it's
not necessary to spend time finding the larvae. After the initial insecticide
application, feeding damage may be from a larva that has already been killed,
so finding the critter is more important for an accurate estimate of the
number of infested plants.

Larvae will leave the tassel as it opens up and no longer provides a
moist, protected feeding environment, and move down the plant looking for
protected places to feed. Insecticide applications need to be timed to
kill larvae before they bore into a new feeding location where they will
be again protected from sprays. In fields with very uneven development,
two applications may be necessary, one when approximately 25-50% if the
tassels have emerged, and again after 75-100% of the tassels have emerged,
if the field is still over threshold.

Once a field reaches the silk stage, the threshold drops to 5% infested
plants. Scout the ear zone (roughly from two leaves above and one leaf below
the ears) for ECB egg masses and ECB or FAW larvae. Egg masses are found
most frequently on the underside of leaves near the midrib, and consist
of approximately 10-20 flattened eggs overlapping like fish scales. Eggs
are white when first laid, turning cream colored after a couple of days,
and show the black head capsules of the tiny larvae through the surface
of the eggs when within 1 day of hatching (the "black head" stage). Egg
masses can also sometimes be found on the flag leaves of the ears or on
the husk itself. Eggs take approximately 100 base 50 degree days to hatch.
When temperatures are in the 70's during the day and the 50's at night egg
masses will take about a week to hatch. When temperatures are in the 80's
during the day and the 60's at night, they could hatch in only 4 days.

Look down into the tops of the silks for newly hatched larvae, and pull
the ear away from the stalk slightly to look for larvae feeding between
the stalk and the ear.

Once CEW are being caught in higher numbers, insecticide applications
in silk stage fields should be determined by CEW trap catches. The recommended
spray intervals for CEW should be adequate for ECB and FAW control. Because
CEW lay their eggs directly on the silk, and eggs are difficult to find
in the field unless the population is VERY high, we rely on pheromone trap
catches rather than scouting to make CEW management decisions. It is most
important to adhere to the recommended spray intervals when the field is
in the green silk stage. The chart below indicates recommended spray intervals
during the silk stage for a range of trap catches:

Average CEW Pheromone Trap Catches

Per Day

Per Five Days

Per Week

Days Between Sprays

<0.2

<1.0

<1.4

No Spray (for CEW)

0.2-0.5

1.0-2.5

1.4-3.5

6 days

0.5-1.0

2.5-5.0

3.5-7.0

5 days

1-13

5-65

7-91

4 days

over 13

over 65

over 91

3 days

Add one day to the recommended spray interval if daily maximum temperatures
are less than 80° F for the previous 2-3 days.

Location

ECB-E

ECB-Z

CEW

FAW

Adams (Jefferson Co.)

NA

NA

NA

NA

Baldwinsville (Onondaga Co.)

NA

NA

NA

NA

Batavia (Genesee Co.)

1

0

0

NA

Bellona (Yates Co.)

1

10

0

4

East Otto (Cattaraugus Co.)

0

0

0

1

Eden Z (Erie Co.)

0

19

4

44

Farmington (Ontario Co.)

1

0

2

0

Hamlin (Monroe Co.)

0

6

10

5

Kennedy (Chautauqua Co.)

0

9

1

5

King Ferry (Cayuga Co.)

NA

NA

NA

NA

Kirkville (Madison Co.)

12

2

1

0

LeRoy (Genesee Co.)

0

0

0

0

Lockport (Niagara Co.)

2

16

6

8

Medina (Orleans Co.)

3

11

0

2

Owego (Tioga Co.)

0

NA

0

NA

Penn Yan (Yates Co.)

2

3

0

4

Spencerport (Monroe Co.)

0

6

4

0

Wayland (Steuben Co.)

NA

NA

NA

NA

Williamson (Wayne Co.)

4

7

0

0

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These pages are maintained by the New York State IPM Program, part of Cornell Cooperative Extension. All material is protected by Section 107 of the 1976 copyright law. Copyright is held by Cornell University and the New York State IPM Program.